320Fall10Lecture12 - 1 BIO 320 Cell Biology, Fall 2010 Dr....

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BIO 320 Cell Biology, Fall 2010 Dr. Thomas Bushart Week 12 1
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Epithelial sheets Epithelial sheets are analogous to membranes in the cell Epithelial cells are polarized Anchored to a basal lamina Free at their apical side Serve as selective permeability barriers Requires sealing through occluding junctions 2
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Epithelial organization 3
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Occluding junctions Tight-sealing junctions found in sheets of epithelial cells Tight junctions in vertebrates Septate junctions in invertebrates Seals gaps between cells Permeability depends on epithelial type Paracellular transport Act as molecular fences 4
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Tight junctions Selectively separate one extracellular space from another 5
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Sealing strands Each strand acts as barrier 6
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Sealing strands Rows of transmembrane adhesion proteins 7
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Tight junction composition Claudins – major transmembrane protein component Different junctions utilize different claudins Certain claudin types may allow for paracellular pore formation (for paracellular transport) Mg 2+ uptake in kidney epithelia, for example Occludin – nonessential, but there Tricellulin – required at intersection of three cells to prevent leakage 8
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Junctional cooperativity Tight junctions typically found apical to adheren and desmosome junctions All three comprise the junctional complex Disruption of caherins also prevents tight junction formation Organization depends on tight junction proteins (Tjp) family members 9
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Septate junctions Invertebrate junction functions the same Proteins more evenly ordered 10
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Gap junctions Direct passages between the cytosol of adjacent cells Small molecules can pass Cell communication and metabolites Electrical coupling 11
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Gap junction structure Clusters of connexons made up of six connexin subunits Each connexin is a 4-pass transmembrane protein 12
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Differing properties Arrangements of various connexins can produce gap junctions with differing properties 13
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Gap junction functions Electrical coupling of excitable cells Synchrony and rapid spread of APs Heart muscle cells and smooth muscles of the intestines Genetic basis for most congenital deafness Coordination of responses Hepatocyte breakdown of glycogen Ovarian follicle development Embryogenesis 14
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Can be open or closed like channels High Ca 2+ shuts off, indication of cell damage? Dopamine reduces communication in some
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320Fall10Lecture12 - 1 BIO 320 Cell Biology, Fall 2010 Dr....

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